View source for Aso Caldera

{{short description|Caldera in Kumamoto Prefecture, Japan}}
{{Expand Japanese|topic=geo|日本の地理|date=January 2020}}
{{Infobox mountain
<!-- *** Heading *** -->
| name= Aso Caldera
| native_name={{native name|ja|阿蘇カルデラ}}
| other_name= Aso Volcano, Asosan
<!-- *** Names **** -->
| etymology=
<!-- *** Image *** -->
| photo= File:Aso Caldera 3D 2012.jpg
| photo_caption=Aso Caldera
| photo_size=
<!-- *** Country *** -->
| country= Japan
| subdivision1= [[Kumamoto Prefecture]]
| subdivision2_type= Region
| subdivision2= [[Aso District, Kumamoto|Aso District]], [[Aso, Kumamoto|Aso City]], [[Takamori, Kumamoto|Takamori]]
| coordinates= {{coord|32.884|N|131.104|E|type:mountain_scale:100000|format=dms|display=inline,title}}
| coordinates_ref=<ref name="GVPData">{{Cite web|url=https://volcano.si.edu/volcano.cfm?vn=282110|title=Asosan {{!}}Global Volcanism Program {{!}} Smithsonian Institution|website=volcano.si.edu|language=en|access-date=2022-09-25}}</ref>
<!-- *** Locations *** -->
| highest=Takadake
| highest_location={{coord|32|53|03|N|131|06|14|E|type:mountain_scale:100000|format=dms|display=inline}}
| elevation_m=1592
<!-- *** Dimensions *** -->
| length_km= 25
| length_orientation= NS
| width_km= 18
| width_orientation= EW
| area_km2=
<!-- *** Features *** -->
| geology= [[Dacite]], [[Andesite]]<ref name="GSJ" />
| orogeny=
| age= [[Pleistocene]] onwards
| type=[[Caldera]]<br />[[Somma volcano]]
| last_eruption= 2021 CE<ref name="E2021" />
<!-- *** Maps *** -->
| map_caption=
| map = Japan
| location = [[Kumamoto]], Japan
}}
{{stack|
[[File:Mt. Aso, Japan.jpg|thumb|Aerial view of Aso Caldera]]
[[File:20140516阿蘇山広域.jpg|thumb|Central cones of [[Mount Aso|Aso volcano]] from their north east]]
[[File:Mt.Aso and caldera01.jpg|thumb|Central cones of [[Mount Aso|Aso volcano]] as seen from the north]]
[[File:MtAso from Takamori.jpg|thumb|Central cones of [[Mount Aso|Aso volcano]] as seen from the south near [[Takamori, Kumamoto|Takamori]]]]
[[File:Aso-zan-nakadake.JPG|thumb|View of the Central cones of [[Mount Aso|Aso volcano]] with Nakadake steaming]]
}}
'''Aso caldera''' (also known as '''Asosan''', the '''Aso Volcano''' or '''[[Mount Aso]]''', although the later term usually is used related to its currently active vents) is a geographical feature of [[Kumamoto Prefecture]], Japan. It stretches 25 kilometers north to south and 18 kilometers east to west. The central core "Aso Gogaku" is the five major mountains in the area. Aso valley (Asodani) runs along the northern base of [[Mount Aso]] and [[Nangō, Miyazaki (Minaminaka)|Nango valley]] (Nangodani) along the south. According to research of caldera sediment, lakes used to exist in these valleys. The dried up lake areas have come to be called Old Aso Lake, Kugino Lake, and Aso Valley Lake. The [[Kikuchi River|Kikuchi]], [[Shirakawa River (Kumamoto)|Shirakawa]] and Kurokawa rivers now drain the caldera.<ref name="AsoGeoPark">{{cite web|url=http://www.aso-geopark.jp/ggn/pdf/annex2.pdf |title=Aso GeoPark Annex 2：Geological Heritage |access-date=2022-09-25}}</ref>
== Geology ==
Within the caldera are more than 17 cones.<ref name="Huang1918">{{cite journal|last1=Huang |first1=YC |last2= Ohkura |first2= T. |last3= Kagiyama |first3= T. |title= Shallow volcanic reservoirs and pathways beneath Aso caldera revealed using ambient seismic noise tomography |journal= Earth Planets Space |volume=70 |issue= 169 |year=2018 |page=169 |doi=10.1186/s40623-018-0941-2 |bibcode=2018EP&S...70..169H |doi-access= free |hdl= 2433/245903 |hdl-access= free }}</ref> The central "Aso Gogaku" group of volcanoes are Takadake (Mount Taka) at {{convert|1592|m|abbr=on}}, Nekodake at {{convert|1433|m|abbr=on}}, Nakadake (Mount Naka) at {{convert|1,506|m|abbr=on}}, Kijimadake at {{convert|1321|m|abbr=on}} and Eboshidake at {{convert|1337|m|abbr=on}}.<ref name="AsoGeoPark" /> These are higher than the caldera rim itself that towards the south west is {{convert|1236|m|abbr=on}} high.<ref name="GSJ">{{cite web|url=https://gbank.gsj.jp/volcano/Quat_Vol/volcano_data/J32.html |title=Aso Caldera |access-date=2022-09-25 }}</ref> Other volcanic features include Kishimadake (Mount Kishima), Kusasenrigahama, Komezuka, a scoria cone, Ikenokubo maar, a tuff ring and Takanooban, a lava dome.<ref name="AsoGeoPark" /> The currently active Nakadake has seven craters roughly aligned in a north–south direction with most recent eruptions being from the northernmost ''first'' crater of Nakadake which has hydrothermal reservoirs beneath it at about {{convert|1|km|abbr=on}} to {{convert|2.5|km|abbr=on}} depth.<ref name="Huang1918" /> Presently there is a roughly spherical [[magma]] chamber at a depth of {{convert|6|km|abbr=on}}, and flattened at {{convert|10|km|abbr=on}} located between Kishimadake, Eboshidake, and Nakadake with the magmatic source beneath the center of Aso caldera.<ref name="Huang1918" /> Magma migrates diagonally upward from approximately {{convert|17|km|abbr=on}} depth through a northward-dipping magma-filled crack propagation zone, then into the shallow magma reservoirs mentioned already and during eruptions into an upright crack intrusion zone at {{cvt|2–4|km}} depth.<ref name="Hata1918">{{cite journal|title=Three-Dimensional Electrical Resistivity Modeling to Elucidate the Crustal Magma Supply System Beneath Aso Caldera, Japan |journal= Journal of Geophysical Research: Solid Earth| url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JB015951 |year=2018 |doi=10.1029/2018JB015951 |first1=M. |last1=Hata|first2= N. |last2=Matsushima |first3= S. |last3=Takakura |first4= M. |last4=Utsugi |first5= T. |last5=Hashimoto |first6= M. |last6=Uyeshima |volume= 123|issue= 8|page= 6334|bibcode= 2018JGRB..123.6334H|s2cid= 135216076}}</ref> There are many geothermal areas including centrally the Jigoku or "hell" Onsen and Tarutama hot springs and in the northern part, the Uchinomaki hot springs.<ref name="AsoGeoPark" />
=== Formation ===
[[File:Aso-4 tephra 90-85ka.svg|thumb|left|Immediate impact of the Aso Caldera forming eruption. The pink pyroclastic flow although sterilising was modified by landforms more than this figure suggests, but 15&nbsp;cm tephra contour did have significant impact on all higher life forms.]]
The [[caldera]] formed from four major [[pyroclastic flow]] events which occurred between 90,000 and 270,000 years ago. The largest of these was the fourth, which reached as far as nearby [[Yamaguchi Prefecture]] 160 kilometers away. The fourth eruption left a massive [[Volcanic plateau|pyroclastic plateau]] which is what remains even today. In 1985 it was discovered that volcanic ash from the fourth eruption covered much of the Japanese islands. The eruptive volume of the fourth eruption is estimated to be {{convert|384|km3|abbr=on}} [[dense-rock equivalent]] (DRE).<ref name="52Aso" /> Ashfall deposit greater than {{convert|15|cm|abbr=on}} deep was identified on [[Hokkaido]] Island about {{convert|1500|km|abbr=on}} to the north.<ref name="Hata1918" />
[[File:Mt.nekodake.jpg|thumb|Nekodake, the most western Central cone within the Aso Caldera]]
=== Eruptions ===
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at:2050 shift:(10,-2) fontsize:XS text:Aso eruptions since written records
at:2040 shift:(10,-2) fontsize:XS text:(Nakadake unless noted otherwise)
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at:1816 shift:(10,-2) fontsize:XS text:July 1816 Yunotani Onsen Disaster 1 dead
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Aso volcano has been active at intervals of approximately 10–20 years with the most active cone in recorded history being Nakadake located in the center of the caldera.<ref name="Huang1918" /> It has been active since the sixth century.<ref name="Hata1918" /> Eruptions occurred from November 2014 to May 2015, with two major phreatomagmatic eruptions on September 14, 2015, and October 8, 2016.<ref name="Huang1918" /> Eruptive activity occurred on 20 October 2021.<ref name="E2021">{{cite web|url =https://www3.nhk.or.jp/nhkworld/en/news/20211020_18/ |title=Mount Aso in Kumamoto erupts|publisher=nhk.or.jp|access-date = October 20, 2021}}</ref>
Main eruption ages and eruption volume (DRE ([[dense-rock equivalent]]) is the equivalent magma eruption volume. The volume of erupted products is much higher):<ref name="JMA">{{cite web|url=https://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/souran_eng/volcanoes/084_asosan.pdf |title=Asosan: National catalogue of the active volcanoes in Japan |access-date=2022-09-25 }}</ref>
* Aso-1: About 266,000 years ago,<ref name="kasai">[https://sh.higo.ed.jp/hsearth/otayori/%E9%98%BF%E8%98%87/%E9%98%BF%E8%98%87%E7%81%AB%E7%A0%95%E6%B5%81%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6 阿蘇火砕流について] {{Webarchive|url=https://web.archive.org/web/20211023075438/https://sh.higo.ed.jp/hsearth/otayori/%E9%98%BF%E8%98%87/%E9%98%BF%E8%98%87%E7%81%AB%E7%A0%95%E6%B5%81%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6 |date=2021-10-23 }} 熊本県高等学校教育研究会 地学部会</ref> erupted {{cvt|32|km3}} DRE.<ref name="52Aso" />
* Aso-2: About 141,000 years ago,<ref name="kasai" /> erupted {{cvt|32|km3}} DRE.<ref name="52Aso">[https://www.gsj.jp/data/openfile/no0613/52Aso.pdf 阿蘇カルデラ]. 産総研</ref>
* Aso-3: About 130,000 years ago,<ref>下山正一、[https://web.archive.org/web/20200114082206/http://portal.dl.saga-u.ac.jp/handle/123456789/13789 低平地地下における阿蘇3火砕流堆積物(Aso-3)の年代について] 佐賀大学低平地防災研究センター編 低平地研究 Vol.10 p.31-38</ref> erupted {{cvt|96|km3}} DRE.<ref name="52Aso" />
* Aso-4: About 90,000 years ago, erupted {{cvt|384|km3}} DRE <ref name="52Aso" /> which was at least [[VEI]] 7.
* Nojiri pumice about 84,000 years ago erupted {{cvt|1|km3}} DRE.<ref name="Miyabuchi2009">{{cite journal|first1=Yasuo |last1=Miyabuchi |title=A 90,000-year tephrostratigraphic framework of Aso Volcano, Japan |journal=Sedimentary Geology |volume=220 |issue= 3–4 |year=2009 |pages=169–189 |issn=0037-0738 |doi=10.1016/j.sedgeo.2009.04.018 |bibcode=2009SedG..220..169M |url= https://www.sciencedirect.com/science/article/pii/S0037073809001006 }}</ref>
* Kusasenrigahama Pumice from Kusasenrigahama at approximately 30,000 years ago<ref name="Huang1918" /> erupted {{cvt|1|km3}} DRE at [[VEI]] 5<ref name="Miyabuchi2009" />
* Jigoku spa about 8,050 BCE, Ikph2 tephra<ref name="JMA" /><ref name="GVPData" />
* Janoo before 5,300 BCE Tephta and scora cone<ref name="JMA" />
* Nakadake 5,300 to 12,000 BCE tephra falls<ref name="JMA" />
* near Janoo about 5,300 BCE Akamizu lava flow<ref name="JMA" />
* Near Ikenokubo about 5,300 BCE tuff ring<ref name="JMA" />
* Jigoku Onsen 3,000 to 4,400 BCE tephra, Ikph1 tephra<ref name="JMA" /><ref name="GVPData" />
* Nakadake 3,000 to 4,400 BCE tephra falls<ref name="JMA" />
* Nakadake 4,000 to 3,000 BCE tephra falls<ref name="JMA" />
* Unknown vent near Janoo, 2150 BCE Aso central cone No. 1 pumice, ACP-1 tephra<ref name="GVPData" />
* Kishimadake 2,050 BCE >{{cvt|0.02|km3}} DME [[VEI]] 4, KsS tephra<ref name="JMA" /><ref name="GVPData" />
* Nakadake 1,600 to 2,000 BCE tephra falls<ref name="JMA" />
* Ojodake 1,650 BCE >{{cvt|0.02|km3}} DME [[VEI]] 4, OjS tephra<ref name="JMA" /><ref name="GVPData" />
* Komezuka, Kamikomezuka 1,350 BCE tephra {{cvt|0.05|km3}} DME<ref name="JMA" />
* Unknown Aso 1270 ± 75 BCE<ref name="GVPData" />
* Western central cones debris avalanche 100 CE to 400 BCE<ref name="JMA" />
* Nakadake 630 ± 50 BCE tephra falls<ref name="JMA" />
* Nakadake 440 ± 75 CE N2S tephra fall<ref name="JMA" /><ref name="GVPData" />
* See timeline for eruptions in historic written record (KEY-pink if confined to volcano, red tephra fall, magenta human deaths)
=== Tectonics ===
There are multiple active faults both under the volcano and adjacent on this area of the [[Amur Plate]]. The [[Okinawa Plate]] collides with the Amur Plate to the south and the [[Pacific Plate]] is subducting under both. The caldera is located where two volcanic lines intersect, being those in the Central Kyushu Rift Valley with volcanoes of [[Mount Yufu]], in [[Oita Prefecture]], through the [[Mount Kujū|Kuju volcanoes]] and Aso Caldera, and on to [[Mount Unzen]] and line that runs from Aso Caldera to the [[Mount Kirishima|Kirishima volcanic group]], [[Aira Caldera]], [[Ata Caldera]], and on to the [[Kikai Caldera]].<ref name="AsoGeoPark" /> The high resolution [[Bouguer anomaly|Bouguer]] [[Gravity anomaly|gravity imaging]] of Kyushu has confirmed the caldera to be piston rather than funnel shaped, as originally proposed, and related to known active faults and in particular the gravity gradient zone of the Aso Caldera is part of the Oita-Kumamoto Tectonic Line (OKTL) gravity gradient zone and this appears to connect with the [[Japan Median Tectonic Line]]s gravity gradient zone, strengthening the evidence that the lines are closely related tectonic features.<ref name="Shichi2005">{{cite book|last1=Shichi |first1= R. |last2=Yamamoto |first2= A. |last3= Kudo |first3= T. |last4= Murata |first4= Y. |last5=Nawa |first5= Kazunari |last6= Komazawa |first6= Masao |last7= Nakada |first7= M. |last8=Miyamachi |first8= H. |last9=Komuro |first9= Hitoshi |last10= Fukuda|first10= Yoichi |last11= Higashi |first11= T. |last12= Yusa |first12= Y.|title= A Window on the Future of Geodesy |chapter= A Gravity Database of Southwest Japan: Application to Bouguer Gravity Imaging in Kyushu District, Southwest Japan |series= International Association of Geodesy Symposia |year=2005 |volume= 128 |doi= 10.1007/3-540-27432-4_40 |url=https://www.researchgate.net/publication/251134851 |pages=236–241 |isbn= 3-540-24055-1 }}</ref>
== Size and other context ==
{{Main|Mount Aso}}
In Japan, the caldera forming [[Lake Kussharo]], which measures {{cvt|26 by 20|km}}, is larger than Aso caldera leaving it the second largest in Japan. It is not rare to see calderas of this scale; however, to see calderas with an interior stable enough to cultivate land, build highways and lay railroads is quite rare. The caldera contains the city of [[Aso, Kumamoto|Aso]] as well as the town and village of [[Takamori, Kumamoto|Takamori]] and [[Minamiaso]].
== References ==
{{reflist}}
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== External links ==
* [https://www.data.jma.go.jp/svd/vois/data/fukuoka/503_Asosan/503_index.html Asosan] – Japan Meteorological Agency {{in lang|ja}}
* [https://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/souran_eng/volcanoes/084_asosan.pdf Asosan: National catalogue of the active volcanoes in Japan] – Japan Meteorological Agency volcanic data
* [https://gbank.gsj.jp/volcano/Act_Vol/aso/index-e.html Aso Volcano] – Geological Survey of Japan – maps
* [https://gbank.gsj.jp/volcano/Quat_Vol/volcano_data/J32.html Aso Caldera] – Geological Survey of Japan – volcano data
* {{cite gvp|name=Asosan|vn=282110|access-date=2021-06-25}}
* [https://www.aso-geopark.jp/en/about/ Aso Geopark]
[[Category:Calderas of Kyushu]]
[[Category:Pleistocene calderas]]
[[Category:Active volcanoes]]
[[Category:Landforms of Kumamoto Prefecture]]
[[Category:Lists of volcanic eruptions]]
[[Category:VEI-7 volcanoes]]
[[Category:Volcanoes of Kyushu]]